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Neuroradiology Case of the Week

Case 457

November 2009

Dhana Rekha Selvaraj, Balasubramanya Kolar, MD,
Henry Wang, MD, PhD and P-L Westesson, MD, PhD, DDS

Clinical Presentation: Patient is a 7-year-old male with right-sided ptosis.

Imaging Findings: On MRI a heterogeneous lesion is seen in the lateral aspect of right orbit, extending into its superior aspect. The lesion is predominantly iso to hyperintense on the T2W images and isointense on the T1W images and shows heterogeneous enhancement. The lesion also appears to extend along the right frontal bone. Minimal proptosis of the right orbit is seen.
     Biopsy of the lesion showed it to be eosinophilic granuloma.

Diagnosis: Eosinophilic granuloma, right orbit

Discussion: Langerhans cell histiocytosis (LCH) is an idiopathic disorder characterized by the proliferation of histiocytes, which are mononuclear cells of the dendritic cell line, derived from bone marrow stem cells and normally found in the epidermis. In LCH, these unique histiocytes form granulomas in conjunction with lymphocytes, polymorphonuclear cells, and eosinophils. Eosinophilic granuloma is a localized form of LCH limited to single or few bones, and is usually seen in older children and young adults, the average age of onset being 10 to 14 years. Males are more commonly affected than females, with a ratio of 2:1. Accounting for approximately 70% of cases of LCH, the localized form is the least aggressive and most favorable expression of the disease [1].
     The histiocytes have abundant eosinophilic cytoplasm and lobulated and grooved nuclei with coffee-bean appearance. The characteristic finding is the presence of Birbeck granules within the cytoplasm. These are rod-shaped or racket-shaped with a central striated line. [2].
     Eosinophilic granuloma is a relatively uncommon entity, accounting for only 1% of all tumorlike lesions of bone [3]. Solitary lesion may occur in any bone, although there is a predilection for the flat bones, with more than half of skeletal lesions occurring in the skull, mandible, ribs, and pelvis [1]. The overall incidence of orbital involvement in a series of 76 children with LCH was 23%. The most common signs and symptoms of orbital LCH were unilateral or bilateral proptosis, edema, erythema of the eyelid, and periorbital pain. Other signs and symptoms were ptosis, optic nerve atrophy, and papilledema. The frontal bone was most commonly involved by LCH and the lesions were usually seen in the superior or superolateral wall of the orbit, in anterior location [2].
     Plain radiographs show lytic bony defects which can be irregular, serrated, beveled, and with or without a narrow zone of sclerosis. In typical cases, CT and MR imaging show an osteolytic lesion, commonly in the superior or superotemporal orbital region. The soft tissue mass can be fairly well-defined or diffuse, encroaching lacrimal gland, lateral rectus, or even the globe. There may be extension of the soft tissue into the epidural space, as well as in the temporal fossa. There may be marked infiltration of temporalis muscles. Multiple lesions may be present resulting in multiple bony defects, particularly in the superolateral and orbital roof regions, other bones of the skull, or in facial bones. Rarely, the lesion may be totally extraosseous. On post-contrast scans, lesions demonstrate moderate to marked enhancement. The differential diagnosis of LCH from an imaging viewpoint includes rhabdomyosarcoma, juvenile fibrosarcoma, aggressive fibromatosis, lacrimal gland tumors, leukemic infiltration, granulocytic sarcoma or chloroma, sinus histiocytosis, metastatic neuroblastoma, metastatic Wilm's tumor, and metastatic Ewing's sarcoma [2].
     In a review of three patients with orbital histiocytosis, consistent findings included a destructive lesion of the lateral wall of the orbit with a large soft-tissue component that extended into the extraconal space, the ocular adnexa, and the infratemporal fossa. The greater wing of the sphenoid was eroded, with epidural extension into the middle cranial fossa. The bone margins were indistinct. No calcification or periosteal new bone formation was present. No intraconal extension was seen [4].
     The treatment options include: follow-up waiting for a spontaneous remission, low-dose radiation for lesions that are extensive and cause optic nerve damage and for lesions which do not improve, cause increasing proptosis, or bone destruction. Other options include partial curettage and intralesional injection of methyl prednisolone [2]. The prognosis is considered to be good for the localized form of the disease. However, approximately 10% of patients presenting with solitary LCH of bone will eventually develop multifocal and extraosseous disease [1].

Conclusion: The diagnosis of eosinophilic granuloma should be considered when a lytic destructive lesion with or without soft tissue mass is seen in the orbit of pediatric patients.

References:

1. Stull MA, Kransdorf MJ, Devaney KO. Langerhans cell histiocytosis of bone. Radiographics. 1992 Jul;12(4):801-23. PMID: 1636041 [PubMed]
2. Hidayat AA, Mafee MF, Laver NV, Noujaim S. Langerhans' cell histiocytosis and juvenile xanthogranuloma of the orbit - clinicopathologic, CT, and MR Imaging features. Radiol Clin North Am. 1998 Nov;36(6):1229-40, xii. PMID: 9884699 [PubMed]
3. David R, Oria RA, Kumar R, et al. Radiologic features of eosinophilic granuloma of bone. AJR Am J Roentgenol. 1989 Nov;153(5):1021-6.PMID: 2801420 [PubMed]
4. Erly WK, Carmody RF, Dryden RM. Orbital histiocytosis X. AJNR Am J Neuroradiol. 1995 Jun-Jul;16(6):1258-61. PMID: 7677020 [PubMed]